BLOOD-PRESSURE RESPONSES TO PHENYLEPHRINE INFUSIONS IN SUBJECTS WITH CUSHINGS-SYNDROME

The pathogenesis of the hypertension associated with Gushing's syndrom e is not completely understood. Sensitivity to presser agents may play a role. We have investigated this possibility by measuring blood pres sure (BP) during incrementally increasing infusions of the alpha-adren ergic agonist phenylephrine. Ten subjects (8 women: 2 men), aged 40 +/ - 5 years (mean +/- s.e.m.) with Gushing's syndrome were studied. All had raised BP but none had received any anti-hypertensive treatment fo r at least 16 days before study. Ten age- (40 +/- 5 years) and sex-mat ched control subjects were also studied. At 13.30, 30 min after a ligh t meal, subjects had an intravenous cannula inserted, ECG leads and a sphygomanometer cuff attached, and then rested supine in a quiet room for 30 min. Phenylephrine was then infused incrementally at intervals of 5 min. The doses used were 0.3, 0.6, 0.9, 1.35 and 2 mu g/kg/min. B asal mean blood pressure (MAP) was 108 +/- 2 mmHg (mean +/- s.e.m.) in patients and 74 +/- 3 mmHg in controls (P < 0.05) and pulse rate was 75 +/- 5 and 68 +/- 3 beats/min (NS), respectively. MAP increased and pulse rate decreased linearly with time. The rate of rise of MAP was 1 .7 +/- 0.4 mmHg/min in subjects and 1.1 +/- 0.2 mmHg/min in controls ( NS). The rate of decrease of pulse was significantly more rapid in Gus hing's subjects than in controls (1.4 +/- 0.2; 0.6 +/- 0.1 beats/min(2 ); P < 0.06). The lack of any increased BP response to alpha-adrenergi c stimulation suggests that altered sensitivity is not a major cause o f the increased BP seen in patients with Gushing's syndrome.